The fuel system in your car or truck delivers the fuel from the gas tank to the engine through a combination of parts, including fuel pump, fuel lines, and filters so just the right amount of clean fuel gets to the engine when it’s needed. When you start your vehicle, the fuel pump begins drawing fuel from the fuel tank and delivers it to the component that controls the fuel-air mixture to the engine, either by carburetor or fuel injector. Any excess fuel that is not used is returned via fuel lines back into the fuel tank.
Although carburetor and fuel injector systems accomplish the same task—getting gas to the engine—they perform somewhat differently.
Carbureted Engines
The fuel system for this type of engine is generally a low-pressure system responsible for mixing the fuel and air together. If equipped with a mechanical fuel pump, the RPMs (revolutions per minute) control how quickly fuel is delivered based on the speed of the car. With an electric fuel pump, the process is basically the same, but some form of restrictor/regulator to ensure that the appropriate amount of fuel is delivered to the combustion chamber where the spark plug ignites it.
Fuel Injected Engines
Most modern cars are fuel injected and depending on the year and make, the level of technology that controls the system may be wiring component controls or a computer. This system is highly pressurized, and the electric fuel pump continuously pumps gasoline at the correct level of pressure. The fuel passes through filters as well as a pressure regulator that ensures correct fuel pressure at the injectors so that the amount of fuel injected into the engine is appropriate for speed and need. Diesel engines are always fuel injected, never carbureted.
Fuel system parts
Every component of your car’s fuel system has a role to play in maintaining your engine’s functionality. Even the lowly gas cap is crucial for fuel injection vehicles to work properly, and a small fuel pump gone bad can bring your vehicle to a standstill!
Fuel cap / Gas cap
The gas cap seals the fill hose and ensures that gas doesn’t spill out of the car in an accident or rollover. The seal or gasket on the gas cap prevents leakage of fuel vapors from the filler neck and keeps the fuel system properly pressurized. Gas caps can be made of plastic, steel, aluminum, and brass with finely calibrated springs and valves and neoprene or polyurethane to ensure a tight seal. Caps are designed with either threads or lugs with a ratcheting mechanism to guarantee a tight seal. Both a bad seal or bent gas cap can lead to problems and a loose or faulty gas cap can cause your car's Check Engine light to come on.
Most fuel tanks, or gas tanks, are located at or under the rear of the vehicle. The fuel tank is the main storage for the gasoline or diesel that runs a car or truck. Some gas tanks incorporate the fuel pump inside rather than attached to the outside. Fuel tanks today have internal baffles (inner walls) to prevent the fuel from sloshing back and forth and to increase the strength and durability of the tank. Gas tanks are made of plastic high-density polyethylene, steel, or aluminum. The material that makes up the gas tank is the auto manufacturer’s choice and depends on the make and model of the vehicle.
Also called the gas cap cover, a fuel filler door protects your gas tank and all its associated parts. These doors can be opened as a spring-push style, actual key lock, or with a door release lever in the driver’s front seat area. In some cases, if the car’s doors are locked, the fuel door will be locked tight until the car doors are unlocked.
Fuel filler neck / Fuel fill hose
The fuel filler neck is the main connector from the gas cap to the fuel tank, the primary point of entry for fuel into a vehicle. It carries fuel from the pump nozzle down to the fuel tank and prevents fuel vapors from escaping during refueling. Fuel filler necks have anti-siphon valves to prevent someone siphoning gas out of the fuel tank.
The fuel pump moves the fuel from the gas tank to the engine. Fuel pumps can be mechanical or electric with all fuel injected cars having electric fuel pumps. Fuel pumps are often located inside the fuel or gas tank but can also be mounted between the engine and the fuel tank, including directly attached to the fuel tank. In spark-ignition engines, the fuel pump transports gasoline from the tank to the fuel bowl where the carburetor mixes the fuel with air and sends it to the engine’s combustion chamber. The electric fuel pump in a fuel injection engine carries fuel by the fuel lines into the fuel injectors, which spray the fuel into the combustion chamber. A car will not start if the fuel pump cannot deliver gasoline from the fuel tank to the engine.
Fuel filter
An engine must have clean fuel for it to function properly and run smoothly. Fuel filters prevent any tiny particles and contaminants from ever reaching the engine and can be located inside the fuel tank feeder fuel line or as a separate inline filter between the fuel tank and the fuel pump.
Fuel lines
The fuel lines connect all your car’s fuel system components with the express purpose of bringing fuel from part to part and ultimately to the engine. Fuel lines are made of different materials, including aluminum, copper nickel, fuel-grade nylon, reinforced rubber, nitrile butadiene rubber, or stainless steel. When choosing the type of replacement fuel lines you need, there are a number of things to consider: type of fuel, PSI rating, flexibility required, inside and outside diameter, length of the line, and durability. Additionally, make sure that you buy a fuel line that can contain both fuel vapor and liquid fuel.
A fuel vapor canister is an emissions control device used in combination with fuel return lines to ensure that gasoline vapors are not released into the air. A critical component of the EVAP system, the canister contains activated charcoal, which absorbs fuel vapors that are then burned off by the engine rather than being released to pollute the atmosphere. Emission controls ensure that the appropriate amount of fuel is delivered, excess fuel is returned to the gas tank, and hazardous vapors are not allowed to escape the system such as scaping vapors discharging the smell of gasoline into the car’s interior or becoming a serious fire hazard if ignited.
The basic types of fuel injection systems are single-point fuel injection, multi-point fuel injection, sequential fuel injection, and direct injection and they are controlled by electric sensors and computers. Fuel injection is a high-pressure system, and a fuel pressure regulator ensures that the system maintains the right pressure by metering the gas pressure between the fuel pump and the fuel injectors. An injector assembly consists of a needle valve, injection nozzle, compressor spring, and an injector body.
Fuel gauge
The fuel gauge in the dashboard registers the amount of fuel in the fuel tank so, a driver always knows the actual amount of fuel in the fuel tank. One quarter of a tank fuel level is a good time to fill up.
Also called a fuel gauge sender or fuel gauge sending unit, a fuel tank send unit is responsible for sending the signal that works the fuel gauge in the dashboard. Located in the fuel tank, it consists of an arm, float, and a resistor that changes according to the fuel level. If your fuel gauge is inaccurate or stuck at full or empty, you may need a new fuel gauge sender.
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